>> Hillary Clinton pneumonia diagnosis surfaces after falling at 9/11 memorial

According to the Los Angeles Times, Clinton campaign spokesman Nick Merrill said Clinton, 68, won't be traveling Monday or Tuesday to California, where she had been scheduled to appear at fundraisers and tape an episode of "The Ellen DeGeneres Show."

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"I take two pictures before she passed me," Zdenek Gazda, who filmed the video, told BuzzFeed. "She looked like everything was fine and everything was good. I just saw the secretary waiting for the van, and the van came, and she (couldn't) walk inside, and she (got) helped. She lost her shoe and everything."

Merrill said Clinton felt "overheated" at the ceremony and was taken to the apartment of her daughter, Chelsea. After resting, Clinton emerged from the apartment, telling reporters, "I'm feeling great."

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According to ABC News, Clinton's doctor, Lisa Bardack, said in a statement later Sunday that Clinton had been diagnosed with pneumonia two days earlier.

“Secretary Clinton has been experiencing a cough related to allergies,” Bardack said. “On Friday, during follow-up evaluation of her prolonged cough, she was diagnosed with pneumonia. She was put on antibiotics, and advised to rest and modify her schedule. While at this morning's event, she became overheated and dehydrated. I have just examined her and she is now re-hydrated and recovering nicely."

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Republican presidential candidate Donald Trump, who has questioned Clinton's "stamina" in the past, has not commented on her illness. Bloomberg reports that his campaign plans to keep quiet about the issue.